+1 for Dinosaur
If you can change your thermostat you can change the circuit board, it's easier to do,
take lots of pictures.
Here is a forum thread that will help. Post #9 has a picture of a furnace/circuit board.
4 screws gets the cover off
4 small screws holds the board in.
Look at the bottom of the board if you see any colors besides green and silver (corrosion is rusty looking) you've found your trouble.
https://www.thorforums.com/forums/f8...sue-20083.html
This is a link to Dinosaur.
https://www.dinosaurelectronics.com
Post #4 is a picture of our circuit board.
https://www.thorforums.com/forums/f8...off-19066.html